<%--
  Created by IntelliJ IDEA.
  User: 云哥
  Date: 2023/6/2
  Time: 11:10
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>empty操作符：判断是否为空</h1>
<h1>欢迎xxx</h1>
<h2>您还未登录！</h2>
<hr>
${empty requestScope.username}
<br>
${not empty requestScope.username}
<br>
${! empty requestScope.username}
</body>
</html>
